1. Field of the Invention
The present invention relates to: a resist underlayer film composition effective especially as an antireflective film material used in microprocessing in manufacturing process of a semiconductor device and so on; a method for producing a polymer for a resist underlayer film composition; and a resist patterning process using the same, wherein the process is suitable for photo-exposure to a light such as a far UV beam, a KrF excimer laser beam (248 nm), an ArF excimer laser beam (193 nm), an F2 laser beam (157 nm), a Kr2 laser beam (146 nm), an Ar2 laser beam (126 nm), a soft X-ray (EUV: 13.5 nm), an electron beam (EB), and an X-ray.
2. Description of the Related Art
As an LSI advances toward higher integration and higher processing speed in recent years, miniaturization of a pattern rule is required. In such a trend, in a lithography using a photo-exposure which is used as a general-purpose technology, various technologies are being developed how to carry out patterning finely and more precisely to a light source used therein.
Photo-exposure using a g-beam (436 nm) or an i-beam (365 nm) of a mercury lamp has been widely used as a light source for a lithography used in the resist patterning; and as a means for further miniaturization, shifting of the exposure light to a shorter wavelength was assumed to be effective. Accordingly, in mass production process of the DRAM (Dynamic Random Access Memory) with a 64 megabits, a KrF excimer laser (248 nm), a shorter wavelength than the i-beam (365 nm), was used in place of the i-beam as the exposure light source. However, in production of DRAM with integration of 1 G or higher which requires a further miniaturized process technology (processing dimension of 0.13 μm or less), a light source with further shorter wavelength is required, and thus, a lithography using especially an ArF excimer laser (193 nm) has been investigated.
In a monolayer resist method which is used as a typical resist patterning process, it is well known that pattern fall occurs during development due to surface tension of a developer if ratio of a pattern height to a pattern line width (aspect ratio) is too high. In the case of forming a pattern with a high aspect ratio on a non-planar substrate, it is known that a multilayer resist method, in which patterning is done by laminating the films having different dry etching properties, is suitable. Accordingly, what have been developed are: a two-layer process in which a resist film of a photo-sensitive silicon polymer and a underlayer film of an organic polymer mainly composed of elements of a carbon, a hydrogen, and an oxygen, such as for example, a novolak polymer, are combined (Patent Document 1, and so on); and a three-layer process in which a resist film of a photo-sensitive organic polymer used in a monolayer resist method, a middle layer film of a silicon polymer or a silicon CVD film, and a underlayer film of an organic polymer are combined (Patent Document 2, and so on).
Because patterning of the underlayer film of the above-mentioned multilayer resist methods is done by dry etching with an oxygen gas by using a silicon-containing material film which is formed immediately thereabove as a hard mask, the underlayer film of an organic polymer mainly composed of elements of a carbon, a hydrogen, and an oxygen is used; and at the same time, the underlayer film is required to have an etching resistance during the time of dry etching of a substrate to be processed, to be able to form a highly flat film on the substrate to be processed, and, depending on its use method, to have an antireflective function during photo-exposure. For example, in Patent Document 2, which describes a technology relating to a underlayer film composition for a two-layer or a three-layer process, when a underlayer film like this is used, not only the underlayer film pattern with high precision can be formed but also a high etching resistance to etching conditions of the substrate to be processed can be secured.
Here, substrate reflectance when k-value (extinction coefficient) of the resist middle layer film is changed is shown in FIG. 2.
When k-value of the resist middle layer film is made 0.2 or lower and film thickness thereof is set appropriately, sufficient antireflective effect of 1% or less can be obtained.
In FIG. 3 and FIG. 4, change of reflectance with change of film thickness of the middle layer film and of the underlayer film in the case of k-value of the underlayer film being 0.2 and 0.6, respectively, is shown. By comparison between FIG. 3 and FIG. 4, it can be seen that, with higher k-value of the resist underlayer film (in the case of 0.6 (FIG. 4)), reflectance can be suppressed to 1% or less with a thinner film. When k-value of the resist underlayer film is 0.2 (FIG. 3), to obtain reflectance of 1% in the film thickness of 250 nm, the resist middle layer film needs to be thicker. If the resist middle layer film is made thicker, load to the uppermost resist film becomes larger during the time of dry etching of the resist middle layer film so that this is not desirable. In FIG. 3 and FIG. 4, reflectance in the dry exposure with NA of the exposure equipment lens being 0.85 is shown, which suggests that reflectance of 1% or less can be obtained, independent of k-value of the underlayer film, by optimizing the n-value (refractive index), the k-value, and the film thickness of the middle layer film of the three-layer process.
On the contrary, when NA of the projection lens becomes 1.0 or more by an immersion lithography, angle of the incident light to the antireflective film becomes shallower. The antireflective film suppresses reflection not only by absorption of the film itself but also by a negating action due to the interference effect of light. The interference effect of the oblique incident light is small thereby increasing the reflectance.
Among the films in the three-layer process, it is the middle layer film that has an antireflective effect due to the interference action of a light. The underlayer film is too thick for the interference action so that there is no antireflective effect by a negating action due to the interference effect. Reflection from surface of the underlayer film needs to be suppressed, so that the k-value needs to be made less than 0.6 and the n-value near to the value of the middle layer film thereabove. If a transparency is too high due to a too small k-value, reflection from the substrate takes place; and thus, in the case that NA of an immersion photo-exposure is 1.3, the k-value is preferably in the range of about 0.25 to about 0.75, or most preferably in the range of about 0.25 to about 0.48. Target n-values of both the middle layer film and the underlayer film are near to 1.7, the n-value of the resist.
As the processed line width becomes narrower, phenomena such as wiggling and bending of the underlayer film during etching of the substrate to be processed by using the underlayer film as a mask have been reported (Non-Patent Document 1). It is generally well known that an amorphous carbon film formed by a CVD method (hereinafter, this film is referred to as “CVD-C film”) can very effectively prevent wiggling from occurring because amount of hydrogen atoms therein can be made extremely small.
However, in the case of a non-planar underlayment substrate to be processed, the difference in levels needs to be made flat by the underlayer film. By making the underlayer film flat, variance in film thickness of the middle layer film and the photoresist formed thereabove can be suppressed so that a focus margin in lithography can be enlarged.
In the CVD-C film using a raw material such as a methane gas, an ethane gas, and an acetylene gas, it is difficult to fill up the difference in levels thereof to flat. On the other hand, in the case that the underlayer film is formed by a spin coating method, concavity and convexity of the substrate can be filled up.
As mentioned above, the CVD-C film is poor in filling-up of the difference in levels, and in addition, introduction of a CVD equipment is sometimes difficult due to its price and occupied footprint area. If a wiggling problem could be solved by using an underlayer film composition capable of forming a film by a spin coating method, process as well as equipment thereof could be simplified.
The underlayer film mentioned above is formed by heat treatment after spin coating (Post Application Bake, hereinafter sometimes “PAB”); and, if a body to be processed has a thermally vulnerable structure or deformation of a wafer needs to be suppressed as much as possible, this PAB temperature needs to be made low (for example, 250° C. or lower). The underlayer film becomes dense by a crosslinking reaction during PAB (for example, Patent Document 2); but if the PAB temperature is too low, this crosslinking reaction is insufficient, thereby causing such troubles as any one of reduction in film thickness due to dissolution of the underlayer film during application of a silicon-containing material film or the like on this underlayer film by spin coating and intermixing between both films near interface of them or both.
As mentioned above, a method for forming an underlayer film having n-value, k-value, and filling-up properties suitable as an antireflective film, having an excellent pattern-bend resistance without wiggling during etching, and having sufficient solvent resistance even with low PAB temperature is wanted.